1. Field of the Invention
The present invention relates to a vertical batch processing apparatus used for removing a semiconductor oxide film present on target objects, such as semiconductor wafers, and a semiconductor processing system including the apparatus. The term “semiconductor process” used herein includes various kinds of processes which are performed to manufacture a semiconductor device or a structure having wiring layers, electrodes, and the like to be connected to a semiconductor device, on a target object, such as a semiconductor wafer or a glass substrate used for an LCD (Liquid Crystal Display) or FPD (Flat Panel Display), by forming semiconductor layers, insulating layers, and conductive layers in predetermined patterns on the target object.
2. Description of the Related Art
In manufacturing semiconductor devices for constituting semiconductor integrated circuits, a target object, such as a semiconductor wafer, is subjected to various processes, such as film formation, oxidation, diffusion, reformation, annealing, and etching. A process of this kind may be performed in a vertical processing apparatus (of the so-called batch type). In this case, semiconductor wafers are first transferred from a wafer cassette onto a vertical wafer boat and supported thereon at intervals in the vertical direction. For example, the wafer cassette can store 25 wafers, while the wafer boat can support 30 to 150 wafers. Then, the wafer boat is loaded into a process container from below, and the process container is airtightly closed. Then, a predetermined process is performed, while the process conditions, such as process gas flow rate, process pressure, and process temperature, are controlled.
In recent years, semiconductor integrated circuits are required to have higher operation speed, increased integration and miniaturization, and smaller film thickness. However, for example, in the case of a film formation process for a thin film, such as a gate insulating film, a semiconductor wafer may have a natural oxide film (consisting of SiO2 if the wafer is Si) formed on the surface before the process. The natural oxide film can cause semiconductor devices to have lower electrical characteristics or to be defective. Accordingly, it is preferable to remove the natural oxide film on the surface of the semiconductor wafer to set the wafer surface in an activated state immediately before the process, and then form a film on the wafer surface in this activated state.
As a method for removing a natural oxide film, there is known a method of the wet process type using HF vapor or diluted HF solution to directly remove a natural oxide film. In this case, the wafer surface unfavorably suffers fluorine left thereon. On the other hand, Jpn. Pat. Appln. KOKAI Publication No. 2003-133284 (Patent document 1) discloses a technique of the dry process type to remove a natural oxide film. According to this technique, a fluorine family etching gas, such as NF3, is caused to react with active species (radicals) generated by plasma to produce an intermediate substance (NHxFy: x and y are positive numbers). Then, the intermediate substance is caused to react with a natural oxide film to form an intermediate film of ammonium silicofluoride [(NH4)2SiF6]. Then, the intermediate film is decomposed or sublimated by heating, and is thereby removed as gas.
In the technique disclosed in Patent document 1, a process chamber and a heating chamber are stacked one on the other and configured to selectively communicate with each other. However, the structure and material of an apparatus for forming ammonium silicofluoride are not clarified. Further, the transfer route of a wafer from carry-in through processing to carry-out is not clarified in relation to a system.
Jpn. Pat. Appln. KOKAI Publication No. 2001-284307 (Patent document 2) discloses another related technique. According to the technique disclosed in Patent document 2, a vertical auxiliary chamber is disposed on one side of a vertical reaction chamber to communicate therewith. H2 gas and N2 gas are supplied into the auxiliary chamber and irradiated with microwaves from above to generate plasma. In this case, however, the gases may be insufficiently activated.
Jpn. Pat. Appln. KOKAI Publication No. 2002-100574 (Patent document 3) discloses another related technique. According to the technique disclosed in Patent document 3, active species and an etching gas are supplied into a vertical process chamber through a lateral side. In this case, the interior of the process chamber is exhausted from the bottom, and the gases may less uniformly flow in the process chamber.